Various liquids and solids, including hazardous liquid and solid materials, are often stored and transported in drums. Such drums are commonly made of plastic, steel or fiber. Drums are typically either of tight head or open head construction; however, open top drums are becoming increasingly popular for shipping both hazardous and nonhazardous materials, largely because they are easy to handle, versatile, and may, in some cases, be nested when empty, thus saving significant storage and shipping space.
In recent years, open top drums made of blow molded or injection molded plastic have come into increasingly frequent use. Plastic open top drums offer the added benefits of being inexpensive, durable and reusable in many applications. Also, plastic drums are nonreactive with a wide variety of contents and are useful for waste disposal applications because they may be loaded with waste material and incinerated easily, with a minimum of energy being required to heat and incinerate the plastic material.
Plastic open top drums and plastic covers therefor are commonly constructed of any of a variety of plastic materials, including but not limited to polyolefins, styrenes, polyethelyne terethalate (PET), polyvinylchloride (PVC), polycarbonate, ABS, nylon polyphenylenes, polyacetals, polyesters and other resins or materials that have adequate Theological properties for blow molding or injection molding and which may be chosen based on the intended use of the drum.
Large size plastic open top drums, e.g., those having capacities in the range of about 30 gallons to about 55 gallons or even greater, were initially developed for the food industry. Later, when applications involving hazardous materials became important, maintaining the integrity of the seal of the drum and cover became of much greater importance than had previously been necessary with respect to drums intended for food applications, as it was necessary to prevent leakage or discharge of hazardous materials during handling and shipment. Accordingly, the United States Department of Transportation ("DOT") developed testing and certification procedures, and promulgated regulations embodying these test and certification requirements, that are applicable to drums for use in transporting hazardous materials.
The test procedures and regulations of the DOT are currently based on the United Nations Recommendations of the Committee of Experts on the Transport of Dangerous Goods. They require, in part, that the drums be subjected to "drop tests" from various heights to insure that the contents of the drum are not ejected when the drum is dropped on its weakest point. Typically, this requires that the plastic drum be dropped from a height of between about two, four and six feet, depending on the type of hazardous material that is to be carried in the drum. The drum is typically dropped in an inverted diagonal orientation so that the impact takes place on the interface between the retaining ring, cover and chime of the drum assembly. Also, the drum is loaded with a desired amount of heavy test material before it is dropped. Whether or not the drum passes the test is determined by whether the contents of the drum are discharged by the impact.
A typical drop test in accordance with the United Nations/DOT specifications is illustrated in FIGS. 2A and 2B. In FIG. 2A, the drum assembly P, which includes a drum body with a cover and retaining ring affixed thereto and which is loaded with a desired weight W, is shown in a first elevated position during an initial portion of a drop test, after the drum has been released and is in free fall prior to impact. FIG. 2B shows the drum assembly P at the point of impact during the drop test, which illustrates an exemplary deformation of the sidewall of the drum body, the retaining ring, and cover when the drum assembly P strikes a floor surface F.
In general, a drum that is intended for use with extremely hazardous materials must retain its contents in a drop test that is conducted from a greater height than is required for drums to be certified for use with less hazardous materials. For example, the most challenging drop test that is prescribed by the DOT/UN regulations is for hazardous materials in the "X" classification, which require that the drum pass a drop test from a height of about six feet. The "Y" classification, which pertains to less hazardous materials, requires passing a drop test conducted from a height of about 4 feet. The still less hazardous "Z" classification requires that the drum pass a drop test from a height of about two feet. The DOT/UN drop testing must be performed after the drum and its contents have been cooled to a temperature of 0.degree. Fahrenheit or less. If a sufficient number of the drums pass the test at the desired impact, then the drums may be certified for carrying a specified weight of the relevant X, Y or Z classification materials. As a general rule it is desirable to maximize the weight of the contents that a drum is certified to contain during transportation.
In addition, the National Motor Freight Council ("NMFC"), which governs the shipment of nonhazardous material by road, and the Uniform Freight Council ("UFC"), which governs shipment of nonhazardous materials by rail, require that open top plastic drums pass a "tip over" test. In this test a drum is filled with water, the cover and retaining ring are secured to the drum, and the drum assembly is tipped over onto a hard surface such as concrete. The drum passes the test if it does not leak its contents as a result of the impact suffered when the drum is tipped over.
FIG. 3 is a sectional side elevation view of the chime portion 20, cover 12 and retaining ring 13 of one drum assembly 10 that is known in the prior art. Typically, the drum body sidewall 14 is topped off by a chime portion 20. The chime portion 20 includes a first chime wall 21 and a substantially vertical second chime wall 22. The first chime wall 21 may extend upwardly and outwardly from the sidewall 14, often at an angle of between about 15.degree. and 30.degree.; however, in recent structures, the first wall 21 extends substantially radially from the axis of the drum 10. It has been found that a substantially radial wall 21 provides improved retention of the retaining ring 13. The cover 12 of the prior art assembly 10 typically includes a peripheral chime engaging structure 23 which is bounded by an external flange 24. The external flange 24 is typically sized so as to fit over and around an upper portion of the second chime wall 22. The peripheral chime engaging portion 23 and first chime wall 21 are typically secured to one another by first and second legs 25 and 26, respectively, of the retaining ring 13. The retaining ring may include an intermediate wall 30 interconnecting the legs 25 and 26; alternatively, the legs 25 and 26 may be connected by a curved wall or other structure. The ring 13 may be made of metal or any of a variety of plastic materials. The bottom leg 26 is sometimes formed so that when the ring 13 is installed on the drum assembly 10, the leg 26 extends in a substantially radially orientation relative to the axis of the drum 10, although various angled configurations may be used.
Also as shown in FIG. 3, the prior art structure typically includes a gasket 31; however, covers 12 are sometimes provided without a gasket. The cover 12 may also include a central disk portion 32 and a dependent skirt 33, which may be reinforced by a plurality of radial ribs 34.
As illustrated in FIG. 3, the construction of many prior art drum assemblies 10 has resulted in a void area 35 near a lower portion 36 of the second chime wall 22 such that the void area 35 circumscribes the exterior periphery of the wall 22 beneath the intermediate band 30 of the ring 13. It has been found that the presence of this void area 35 may permit the ring 13, and in particular, the lower leg 26 thereof, to shift when the ring 13, cover 12 and chime portion 20 of the drum body 11 are deformed by an impact as illustrated in FIG. 2B.
Previous open top plastic drum, cover and retaining ring structures of the type illustrated in FIG. 3, as well as others, have passed the drop and tip over tests at certain loading weights. However, the weights at which such drums have passed these tests are limited. As it is desirable to maximize the certification conditions at which a drum may be used to transport materials under the applicable regulations, it is desirable to increase the weight that a drums will retain while passing the drop and tip over tests.
In accordance with the foregoing, one object of the present invention is to provide an open top drum chime, having an improved chime structure so that the drum cover and receiving ring assembly will remain intact during the drop and tip over tests at increased loading weights so as to attain higher DOT/UN and NMFC/UFC certifications.
Another object of the invention is to provide a drum assembly which has improved drop test performance without significantly increasing the cost of producing the drum assembly, either by increased material usage or the need for extensive new tooling.
Another object of the invention is to provide a blow molded open top drum assembly having improved drop test characteristics that may be produced without significantly increased production cycle times or undesirable deformation of the sidewall of the drum body while the plastic material is cooled following the blow molding operation.
Yet another object of the invention is to provide a plastic drum assembly that has improved drop test characteristics but which does not have significantly increased mass which might increase the thermal energy that would be required to incinerate the drum.
A further object of the present invention is to provide a blow molded open top plastic drum having improved cover retention characteristics which may be produced with only nominal modification of existing molding equipment.
A still further object of the present invention is to provide a means for stiffening the chime portion of an open top plastic drum without the use of compression molding techniques.
A further object of the present invention is to provide a drum assembly in which void areas between the cover, retaining ring and drum chime are substantially filled so as to prevent shifting of the retaining ring and cover when the drum assembly is drop tested or otherwise subjected to impact.
Yet another object of the present invention is to provide an open top drum having improved cover retention characteristics which may be handled with existing parrot beak type equipment.